2017
Publication Year
2020-09-14T14:36:54Z
Acceptance in OA@INAF
Deuterated methanol on a solar system scale around the HH212 protostar
Title
Bianchi, E.; CODELLA, CLAUDIO; Ceccarelli, C.; Taquet, V.; Cabrit, S.; et al.
Authors
10.1051/0004-6361/201731404
DOI
http://hdl.handle.net/20.500.12386/27364
Handle
ASTRONOMY & ASTROPHYSICS
Journal
606
Number
DOI:10.1051/0004-6361/201731404 c ESO 2017
Astronomy
&
Astrophysics
Letter to the Editor
Deuterated methanol on a solar system scale
around the HH212 protostar
E. Bianchi
1, 2, C. Codella
1, C. Ceccarelli
3, 4, 1, V. Taquet
1, S. Cabrit
5, F. Bacciotti
1, R. Bachiller
6, E. Chapillon
7, 8,
F. Gueth
8, A. Gusdorf
9, B. Lefloch
3, 4, S. Leurini
10, L. Podio
1, K. L. J. Rygl
11, B. Tabone
5, and M. Tafalla
6 1 INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italye-mail: ebianchi@arcetri.astro.it
2 Università degli Studi di Firenze, Dipartimento di Fisica e Astronomia, via G. Sansone 1, 50019 Sesto Fiorentino, Italy 3 Univ. Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France 4 CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France
5 LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06,
École Normale Supérieure, 75014 Paris, France
6 IGN, Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain
7 Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France 8 IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
9 LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, École Normale
Supérieure, 75005 Paris, France
10 INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
11 INAF–Istituto di Radioastronomia & Italian ALMA Regional Centre, via P. Gobetti 101, 40129 Bologna, Italy
Received 19 June 2017/ Accepted 14 September 2017
ABSTRACT
Context. Deuterium fractionation is a valuable tool for understanding the chemical evolution during the process that leads to the formation of a Sun-like planetary system.
Aims.Methanol is thought to be mainly formed during the prestellar phase, and its deuterated form keeps a memory of the conditions at that epoch. The unique combination of high angular resolution and sensitivity provided by ALMA enables us to measure methanol deuteration in the planet formation region around a Class 0 protostar and to understand its origin.
Methods.We mapped both the13CH
3OH and CH2DOH distribution in the inner regions (∼100 au) of the HH212 system in Orion B.
To this end, we used ALMA Cycle 1 and Cycle 4 observations in Band 7 with angular resolution down to ∼000.15.
Results.We detected 6 lines of13CH
3OH and 13 lines of CH2DOH with upper level energies of up to 438 K in temperature units. We
derived a rotational temperature of (171 ± 52) K and column densities of 7 × 1016cm−2(13CH
3OH) and 1 × 1017cm−2(CH2DOH),
respectively. This yields a D/H ratio of (2.4 ± 0.4) × 10−2, which is lower by an order of magnitude than previously measured values
using single-dish telescopes toward protostars located in Perseus. Our findings are consistent with the higher dust temperatures in Orion B with respect to the temperature derived for the Perseus cloud. The emission traces a rotating structure extending up to 45 au from the jet axis, which is elongated by 90 au along the jet axis. So far, the origin of the observed emission appears to be related with the accretion disc. Only higher spatial resolution measurements will be able to distinguish between different possible scenarios, however: disc wind, disc atmosphere, or accretion shocks.
Key words. stars: formation – ISM: molecules – ISM: individual objects: HH212 – ISM: abundances
1. Introduction
Molecular deuteration is a powerful diagnostic tool for study-ing the past history of the gas associated with the formation of a proto-Sun and its protoplanetary system (see e.g. Ceccarelli et al.2014, and references therein). In the prestellar core phase, the low temperatures and the resulting CO freeze-out enhance the abundance of the deuterated molecules. These molecules are stored in the icy grain mantles and are then released into the gas phase in the protostellar stage (Ceccarelli et al.2007; Caselli et al. 2008). This is the case of methanol (CH3OH), which is
formed on the grain surfaces (e.g. Tielens 1983; Rimola et al. 2014) and is then released into the gas phase because dust man-tles are thermally evaporated in the inner warm regions around
low-mass protostars (e.g. Ceccarelli et al. 2000, 2007; Parise et al. 2002, 2004, 2006) and/or sputtered by shocks (Codella et al.2012; Fontani et al.2014).
Deuterated methanol has been analysed towards Class 0 pro-tostars (Parise et al.2006): the measured D/H of 0.4–0.6 indi-cates that CH2DOH can be almost as abundant as CH3OH. In
the only other more evolved source studied so far, the same ra-tio appears to be lower (D/H ∼ 1–7 × 10−3), suggesting a de-crease in deuterated species that is due to evolutionary effects (Bianchi et al.2017). However, all the existing observations have been performed with single-dish telescopes (angular resolution ≥1000), which do not distinguish the different components
associ-ated with a protostellar system (jet, high-velocity shocks, slower accretion shocks, and inner envelope). Sub-arcsecond resolution
A&A 606, L7 (2017)
observations are then crucial to measure the D/H ratio within 50–100 au from the protostar, that is, in the region hosting the protoplanetary discs. Dust grains and ices may also be affected by the accretion shock near the centrifugal barrier, therefore we do not know the deuterium fractionation at small scales.
The HH212 star-forming region in Orion (d= 450 pc) is an ideal laboratory for studying the jet-disc system. The HH212-mm Class 0 protostar is driving a bright, extended, and bipo-lar molecubipo-lar jet extensively observed using IRAM-NOEMA, SMA, and ALMA (e.g. Lee et al.2006,2007,2008,2015, 2016, 2017a,b; Codella et al.2007; Cabrit et al.2007,2012). A molec-ular disc was revealed in HCO+, C17O, and SO emission, using the first ALMA cycles with angular resolutions of ∼000. 6.
Veloc-ity gradients have been detected along the equatorial plane con-sistent with a rotating disc around a 0.2–0.3 M protostar (Lee
et al.2014; Codella et al.2014; Podio et al.2015). A disc with a radius of 60 au has indeed been imaged by Lee et al. (2017a), who observed the dust continuum emission at 850 µm. Finally, Codella et al. (2016) and Leurini et al. (2016) suggested that HDO and CH3OH emission is likely associated with outflowing
gas, and possibly with a disc wind. To conclude, the HH212 re-gion is the unique Class 0 protostellar rere-gion where a bright jet, a compact rotating disc, and signatures of a disc wind have been revealed. In this Letter, we exploit ALMA Band 7 observations with an angular resolution down to 000. 15 to obtain the first
mea-surement of methanol deuteration in the disc formation region.
2. Observations
HH212 was observed in Band 7 with ALMA using 34 12 m an-tennas between 15 June and 19 July 2014 during the Cycle 1 phase. Further observations of HH212 were performed in Band 7 with ALMA using 44 12 m antennas between 6 October and 26 November 2016 during the Cycle 4 phase. The maximum baselines for Cycle 1 and 4 were 650 m and 3 km, respectively.
In Cycle 1 the spectral windows between 337.1–338.9 GHz and 348.4–350.7 GHz were observed using spectral channels of 488 kHz (0.42–0.43 km s−1), subsequently smoothed to
1.0 km s−1. Calibration was carried out following standard proce-dures, using quasars J0607-0834, J0541–0541, J0423–013, and Ganymede. The continuum-subtracted images have clean-beam FWHMs from 000. 41 × 000. 33 to 000. 52 × 000. 34 (PA = −63◦), and an
rms noise level of 5–6 mJy beam−1 in the 1.0 km s−1 channels. For Cycle 4 spectral units of 977 kHz (0.87 km s−1) were used
to observe the spectral windows between 334.1–336.0 GHz. Calibration was carried out following standard procedures, us-ing quasars J0510+1800, J0552+0313, J0541–0211, and J0552– 3627. The continuum-subtracted images have a typical clean-beam FWHM of 000. 15 × 000. 12 (PA = −88◦) and an rms noise
level of 1 mJy beam−1 in the 0.87 km s−1 channels. Spectral line imaging was achieved with the CASA package, while the data analysis was performed using the GILDAS1package. Po-sitions are given with respect to the MM1 protostar continuum peak located at α(J2000) = 05h 43m 51s.41, δ(J2000) = –01◦
0205300. 17 (Lee et al.2014). Lines were identified using
spectro-scopic parameters extracted from the Jet Propulsor Laboratory (JPL2, Pickett et al.1998) and the Cologne Database for Molec-ular Spectroscopy (CDMS3; Müller et al.2001,2005).
1 http://www.iram.fr/IRAMFR/GILDAS 2 https://spec.jpl.nasa.gov/
3 http://www.astro.uni-koeln.de/cdms/
Fig. 1. Left panel: HH212 protostellar system as observed by ALMA-Band 7 (Codella et al.2014). Blue and red contours plot the blue- and redshifted SiO(8–7) jet overlaid on the continuum at 0.9 mm (black con-tours). Positions are with respect to the coordinates reported in Sect. 2. The filled ellipse shows the synthesised beam (HPBW): 000.61 × 000.45.
Central panels: zoom-in of the central region as observed by ALMA-Band 7 Cycle 1:13CH
3OH(130,13–121,12)E and CH2DOH(90,9–81,8)e0
integrated over ±4 km s−1with respect to the v
sys= +1.7 km s−1, (black
contours and grey scale). First contours and steps are 5σ for13CH 3OH
(15 mJy beam−1km s−1) and CH
2DOH (35 mJy beam−1km s−1). The
HPBWs are 000.52 × 000.34 (PA = −64◦
) for13CH
3OH and 000.54 × 000.35
(PA= −65◦
) for CH2DOH. Right panel: zoom-in of the central region,
as observed by ALMA-Band 7 Cycle 4, showing the13CH
3OH(121,11–
120,12)A emission integrated over 10 km s−1around vsys(black contours
and grey scale). First contours and steps are 5σ (20 mJy beam−1km s−1)
and 3σ, respectively. The HPBW is 000.15 × 000.12 (PA = −88◦
).
3. Results and discussion
3.1. Line spectra and maps
In Cycle 1 data, we detected 5 lines of13CH
3OH and 12 lines of
CH2DOH covering excitation energies, Eup, from 17 to 438 K
(see Table A.1). In addition, in the Cycle 4 dataset we re-vealed one transition of13CH3OH (Eup = 193 K) and one of
CH2DOH (Eup = 327 K). Examples of the detected line
pro-files are shown in Fig.A.1: the emission peaks at velocities be-tween '+1 km s−1and+3 km s−1, consistent with the systemic velocity of +1.7 km s−1 (Lee et al. 2014), when the spectral
resolution of 1 km s−1 is considered. The profiles, fit using the GILDAS package, are Gaussian with typical full width at half-maximum (FWHM) ∼5 km s−1. The spectral parameters of the detected lines are presented in TableA.1. Figure 1 introduces the HH212 system: the 0.9 mm continuum traces the envelope hosting the protostar. The bipolar blue- and red-shifted lobes are traced by SiO (Codella et al.2007; Lee et al. 2014). The cen-tral panels, covering a zoom-in of the cencen-tral protostellar region (.000. 5, i.e. 225 au), show the Cycle 1 data, specifically, examples
of the emission maps of13CH3OH and CH2DOH. The emission
is spatially unresolved with a size smaller than the Cycle 1 beam (000. 5 × 000. 3), corresponding to a size of 225 × 135 au. However,
the definitely higher angular resolution provided by the Cycle 4 dataset (000. 15×000. 12 corresponding to a radius of 34 × 27 au)
pro-vides spatially resolved images of the13CH
3OH and CH2DOH4
emission lines. We used the13CH
3OH emission as revealed in
the Cycle 4 image to show in the right panel of Fig.1a further zoom-in, sampling the inner 100 au.
4 The CH
2DOH line is blended with the SO2(82,6–71,7) line
(TableA.1). L7, page 2 of7
3.2. Methanol deuteration
We used the 13CH3OH lines detected in Cycle 1 to perform a
rotation diagram analysis, assuming local thermal equilibrium (LTE) conditions and optically thin lines. In order to exclude opacity effects, we used the13CH
3OH lines to derive the CH3OH
column density because the main isotopologue lines observed by Leurini et al. (2016) are moderately optically thick (τ < 0.4). We also verified that the CH2DOH transitions are indeed
op-tically thin using a population diagram analysis (Goldsmith & Langer1999) in which opacities are self-consistently computed. We used13CH3OH and CH2DOH lines extracted from the same
ALMA dataset in order to have the same u − v coverage and to minimise calibration effects. Moreover, the Cycle 0 (beam '000. 6) observations of CH
3OH (Leurini et al.2016) trace a much
warmer component dominated by lines with Eup up to 747 K
with respect to the emission lines analysed in this paper. A source size of 000. 19 ± 000. 02 has been derived from the13CH
3OH
Cycle 4 map integrated over the whole emission range and then used to correct the Cycle 1 observed values. This value is in good agreement with ∼000. 2, as derived from CH
3OH (Leurini
et al.2016). Figure A.2shows the derived rotational tempera-ture and column density, which are Trot = (171 ± 52) K and
Ntot= (6.5 ± 2.1) × 1016cm−2, respectively. Conservatively, we
used only Cycle 1 data to perform the fit; however, the13CH 3OH
Cycle 4 line is in good agreement with Cycle 1 observations. In the lower panel of Fig.A.2we derive the column density of CH2DOH, assuming the same rotational temperature and size
derived for 13CH
3OH. We excluded from the fitting the two
CH2DOH transitions with Eup> 300 K to exclude any possible
contamination from non-thermal excitation processes or the oc-currence of a component with a different higher excitation con-dition. However, the fitting obtained with the low-energy tran-sitions (continuous line) is in agreement with the two excluded transitions, as well as with the Cycle 4 transition, as shown by the dotted line. The derived column density for CH2DOH is then
Ntot= (1.1 ± 0.2) × 1017cm−2. We note that an LVG analysis (see
Ceccarelli et al.2003, for further details) of the13CH
3OH
emis-sion indicates a source size of 000. 1–000. 2, T
kinlarger than 100 K
and densities higher than 106cm−3, in agreement with the HDO results reported by Codella et al. (2016).
The column densities derived from the rotation diagrams were used to derive the methanol D/H for the first time in the inner 100 au around a low-mass protostar. When we assume a
12C/13C ratio of 70 (Milam et al.2005) at the galactocentric
dis-tance of HH212 (∼8.3 kpc), the D/H is (2.4 ± 0.4) × 10−2. This
value is in agreement with the upper limit of 0.27 derived by Lee et al. (2017b) using CH2DOH and three lines of CH3OH.
In addition, our measurement is lower than previous values of CH2DOH in other Class 0 objects performed with the IRAM
30 m single dish, which indicate D/H ' 40–60% (Parise et al. 2006). Taking into account that as reported by Belloche et al. (2016), the column densities of CH2DOH derived in Parise et al.
(2006) were overestimated by a factor ∼2 because of a prob-lem in the spectroscopic parameters, the HH212 deuteration is still one order of magnitude lower. What are the reasons of this difference? To start with, the single-dish measurements by Parise et al. (2006) are sampling regions ≥2000 au: the D/H is calcu-lated assuming that the main isotopologue and the deuterated species come from the same emitting source, but this cannot be verified with low angular resolutions. This issue is overcome with high angular resolution observations, like those presented here, which allow us to directly image the emitting region. Inter-estingly, Jørgensen et al. (2016) reported a level of deuteration
for glycolaldehyde of ∼5% in IRAS 16293 in Ophiuchus on a scale of 50 au. That said, a possible explanation for the lower methanol deuteration measured for HH212 mm could be related to different physical conditions during the formation of methanol on dust mantles during the prestellar phase. A higher gas tem-perature reduces the atomic gas D/H ratio landing on the grain surfaces and in turn reduces the deuteration of methanol. All the sources observed by Parise et al. (2006) are located in the Perseus star-forming region, which could have had experienced different conditions with respect to the Orion B region where HH212 lies. Specifically, while in Perseus the dust temperature is about ∼12 K (Zari et al.2016), HH212 is located about one degree north of the high-mass star-forming region NGC 2024, and the dust temperature here is ≥16 K (Lombardi et al.2014). As shown by Taquet et al. (2012,2014), for instance, after the volume density is fixed, deuteration (including that of methanol) decreases as temperature increases. The models indicate that D/H can decrease by up to one order of magnitude by increas-ing the temperature from 10 K to 20 K. Interestincreas-ingly, we note that according to Fuente et al. (2014), the methanol deutera-tion in the hot core in the intermediate-mass star-forming region NGC 7129, FIRS 2 is ∼2%. However, in hot cores associated with massive star-forming regions in Orion (Peng et al.2012), the methanol D/H is between 0.8 × 10−3and 1.3 × 10−3, which is lower by one order of magnitude than the values reported here. 3.3. Emitting region of deuterated methanol
Figure2shows the channel maps of the two transitions observed during ALMA Cycle 4, that is, at the highest spatial resolu-tion presented here: 13CH3OH (121,11–120,12)A and CH2DOH
(162,15–161,15)o1 (see Table A.1). For both lines the rightmost
panels show the spatial distributions of the emission close to the systemic velocity. The remaining panels are for the blue- and redshifted velocities, imaged up to ±4 km s−1. We note that for
CH2DOH the redshifted emission is partially contaminated by
the SO2(82,6–71,7) emission (see TableA.1and Fig.A.1).
The spatial distribution of the methanol isotopologues at the systemic velocity is elongated along the jet axis (PA = 22◦). A fit in the image plane gives for 13CH3OH a
beam-deconvolved FWHM size of 000. 18(000. 02) × 000. 12(000. 02) at PA =
33◦. For CH2DOH we derived 000. 20(000. 02) × 000. 10(000. 02) and
PA= 19◦. These values correspond to FWHM sizes of 81 × 54 au
(13CH
3OH) and 90 × 45 au (CH2DOH). Closer to the blue- and
redshifted emission, we resolve a clear velocity gradient parallel to the equatorial plane (see also Fig.A.3) with shifts of ±000. 1 =
45 au, in the same sense as the HH212 disc rotation. The typ-ical (beam-deconvolved) size of the blue- and redshifted emis-sion at ±2 km s−1 from systemic is 000. 22(000. 04) × 000. 14(000. 04)
and 000. 18(000. 02) × 000. 10(000. 03), respectively, similar to the size at
Vsys. Rotation has previously been noted in CH3OH by Leurini
et al. (2016) from unresolved maps at lower resolution ('000. 6).
The authors further noted that emission centroids (fitted in u − v plane) moved away from the source, and eventually away from the mid plane, at higher velocity, speculating that the methanol emission is not dominated by a Keplerian disc or the rotating-infalling cavity, and possibly associated with a disc wind. With the present images we reach higher angular resolution, which allows us to refine the picture: the systemic velocity appears to arise mainly from two peaks at ±000. 05 = 20 au above and
below the disc plane (of which the centroids in Leurini et al. 2016only traced the barycentre). In addition, channel maps at ±1 km s−1suggest redshifted emission peaking in the north and blueshifted emission peaking in the south, which is not the sense
A&A 606, L7 (2017)
Fig. 2. Channel maps of the13CH
3OH(121,11–120,12)A (upper panels) and CH2DOH(162,15–161,15)o1 (lower panels) blue- and redshifted
(contin-uum subtracted) emissions observed during ALMA-Cycle 4 towards the HH212 mm protostar. Each panel shows the emission integrated over a velocity interval of 1 km s−1shifted with respect to the systemic velocity (see the magenta channel, sampling the velocity between+1.5 km s−1
and+2.5 km s−1) by the value given in the upper-right corner. The black cross (inclined in order to point the SiO jet direction and consequently the
equatorial plane, see Fig. 1) indicates the position of the protostar. The ellipse in the top left panel shows the ALMA synthesised beam (HPBW): 000.15 × 000.12 (PA = –88◦
). First contours and steps correspond to 3σ (2.7 mJy beam−1km s−1). Note that for CH
2DOH at velocities higher than
+1.0 km s−1a further emission appears along the jet axes to the north and to the south with respect to the CH
2DOH emission. This is due to the
SO2(82,6–71,7) emission line (see Table 1 and Fig. 2), which has been confirmed to be a good tracer of outflowing material (Podio et al.2015).
Given that the velocity scale has been derived by first fixing the CH2DOH frequency, the SO2 emission looks artificially red, but it is clearly
blueshifted (see Fig. A.1).
we would naively expect for a wind from HH212 mm. Since the jet axis is so close to the plane of the sky5, this might perhaps still be explained by non-axisymmetric structure in a disc wind, but synthetic predictions would be needed to test this. Alterna-tively, our data suggest that the emission could arise from accre-tion shocks occurring at the centrifugal barrier associated with the accretion disc, and heating the gas at temperatures around 100 K (Sakai et al. 2014; Oya et al.2016). The radial extent ∼50 au of the observed red- and blueshifted emission is indeed consistent with the dust disc radius ∼60 au, recently resolved by Lee et al. (2017a) at 850 µm with ALMA. In this case, we would observe a thicker accretion shock near the centrifugal barrier in HH212, as recently seen in C2H in L1527 (Sakai et al.2017).
We may also have a contribution from a warm disc atmosphere, emitting in the northern/southern portions of the accretion disc, thicker than the dust atmosphere.
4. Conclusions
The ALMA Cycle 1 and 4 observations allow us to measure methanol deuteration in the inner 50 au of the jet-disc system associated with the Class 0 protostar HH212, in Orion B. The deuteration is '2 × 10−2, a value lower than has previously been
measured using single-dish telescopes towards Class 0 protostars in Perseus. Although we cannot exclude that single-dish obser-vations are mixing different gas components with different D/H values, our findings are consistent with a higher dust temperature in Orion B than in the Perseus cloud. This confirms the diagnos-tic value of molecular deuteration for recovering the physical conditions during the pre-collapse phase. The emission is con-fined in a rotating structure that extends at ±45 au from the equa-torial plane and is elongated along the jet axis. Disc wind, disc atmosphere, and accretion shocks could explain the observed im-ages. Higher spatial resolution maps are necessary to distinguish between these possibilities.
5 The system inclination is 4◦
to the plane of sky (Claussen et al.1998).
Acknowledgements. We thank C.-F. Lee for instructive comments and sug-gestions. We also thank the anonymous referee for having improved the manuscript. This paper makes use of the ADS/JAO.ALMA#2012.1.00997.S and ADS/JAO.ALMA#2016.1.01475.S data (PI: C. Codella). ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Re-public of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work was supported (i) by the Italian Ministero dell’Istruzione, Università e Ricerca (MIUR) through the grant Progetti Premiali 2012 – iALMA (CUP C52I13000140001); and (ii) by the program PRIN-MIUR 2015 STARS in the CAOS (Simulation Tools for Astrochemical Reactivity and Spectroscopy in the Cyberinfrastructure for Astrochemical Organic Species, 2015F59J3R, MIUR e della Scuola Normale Superiore). M.T. aknowledges partial support from the project AYA2016-79006-P.
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Appendix A: Additional material
Table A.1 lists all the methanol isotopologue lines observed towards HH212 mm during ALMA Cycle 1 and Cycle 4 op-erations. Figure A.1 shows examples of line profiles in TB
scale, while Fig.A.2shows the rotation diagrams for13CH 3OH
and CH2DOH. FigureA.3shows the13CH3OH(121,11–120,12)A
spectrum extracted at ± 000. 06 from the protostar, in the equatorial
plane direction.
Table A.1. Emission lines detected in ALMA Cycle 1 and 4 measure-ments towards HH212 mm. Transition νa E upa Sµ2a rms Fintb (GHz) (K) (D2) (K) (K km s−1) 13CH 3OH Cycle 1 130,13–121,12A 338.75995 206 13 0.29 9.6(1.1) 134,9–143,11E 347.78840 303 4 0.36 4.0(1.4) 110,11–101,9E 348.10019 162 5 0.84 7.5(3.0) 11,1–00,0A 350.10312 17 2 1.16 7.4(3.0) 81,7–72,5E 350.42158 103 2 0.93 8.7(2.6) CH2DOH Cycle 1 90,9–81,8e0 337.34866 96 6 0.15 15.3(0.5) 91,8–82,6o1c 338.46254 120 2 0.26 10.7(2.1)c 131,12–120,12e0 338.86898 202 2 0.13 9.7(0.4) 61,6–50,5e0 338.95711 48 5 0.29 16.7(0.9) 184,15–183,15e1 347.76728 438 10 0.09 6.6(0.3) 184,14–183,16e1 347.95281 438 10 0.18 6.4(0.6) 41,3–40,4e1 348.16076 38 4 0.15 18.1(0.5) 74,4–73,4e1 349.95168 132 3 0.16 25.3(0.5) 74,3–73,5e1 349.95272 132 3 64,3–63,3e1 350.02735 117 2 0.23 19.5(0.7) 64,2–63,4e1 350.02777 117 2 54,2–53,2e1 350.09024 104 2 0.63 20.0(2.2) 54,1–53,3e1 350.09038 104 2 62,5–51,5e1c 350.45387 72 4 0.63 17.0(3.9)c 51,4–50,5e1 350.63207 49 5 0.60 21.0(2.0) 13CH 3OH Cycle 4 121,11–120,12A 335.56021 193 23 0.81 61.7(2.7) CH2DOH Cycle 4 162,15–161,15o1d 334.68395 327 8 0.67 51.1(2.9)d
Notes.(a)Frequencies and spectroscopic parameters are extracted from
the Jet Propulsion Laboratory molecular database (JPL, Pickett et al. 1998) and from the Cologne Database for Molecular Spectroscopy (CDMS, Müller et al. 2001). Upper level energies refer to the ground state of each symmetry.(b) Gaussian fit.(c) The line transition (9
1,8–
82,6)o1 is partially blended with the (7−5,2–6−5,1)E1 CH3OH
transi-tion. The line (62,5–51,5)e1 is partially blended with the (181,17–171,16)E
CH3CHO transition. (d) The CH2DOH (162,15–161,15) o1 line (Eu =
327 K, Si jµ2= 8 D2) is partially blended with the SO2(8–7) transition.
Fig. A.1. Examples of line profiles in TB scale (not corrected for the
beam dilution): species and transitions are reported. The vertical dashed line stands for the systemic VLSRvelocity (+1.7 km s−1, Lee et al. 2014).
Red and blue curves are for the Gaussian fit. In the spectrum of the Cycle 1 (11,1–00,0)A13CH3OH transition, a CH2DOH doublet
contain-ing the (54,2–53,2)e1 and the (54,1–53,3)e1 transitions is also shown (see
TableA.1). In Cycle 4 spectra the (71,7–61,6)A CH3OH and the (82,6–
71,7) SO2transitions are also shown.
0 50 100 150 200 250 300 350 Eup(K) 28.0 28.5 29.0 29.5 30.0 30.5 31.0 ln( Nup /gup ) 13CH 3OH source size = 0.19" T= 171 (52) K N= 6.5 (2.1) x 1016 cm−2 Cycle 1 Cycle 4 0 100 200 300 400 500 Eup(K) 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 ln( Nup /gup ) CH2DOH source size = 0.19" assumed T= 171 (52) K N= 1.1 (0.2) x 1017 cm−2 Cycle 4 Cycle 1
Fig. A.2. Rotation diagrams for13CH
3OH (upper panel) and CH2DOH
(lower panel). An emitting region size of 000.19 is assumed (see text).
The parameters Nu, gu, and Eup are the column density, the
degener-acy, and the energy of the upper level, respectively. The derived value of the rotational temperature is reported for13CH
3OH. For CH2DOH
the Trot derived from the13C-isotopologues is assumed to derive the
column density. The two CH2DOH transitions with excitation energies
higher than 400 K as well as the Cycle 4 point are excluded from the fit, although they are in good agreement with it.
Fig. A.3. Comparison in flux density and in TB scales (TB/Fν =
482.609 K Jy−1) between the 13CH
3OH(121,11–120,12)A spectrum
ex-tracted at ±000.06 from the protostar (see Fig. 2: blue- and redshifted
emission towards north-west and south-east, respectively) in the direc-tion along the equatorial plane (i.e. disc plane; Lee et al. 2017). The vertical dashed line stands for the systemic VLSRvelocity (+1.7 km s−1,
